refactor template stats endpoint to read from new redis keys

New redis keys are partitioned per service per day. New process is as
follows:

* require a count of days to filter by. Currently admin always gives 7.
* for each day, check and see if there's anything in redis. There won't
  be if either a) redis is/was down or b) the service didn't send any
  notifications that day
  - if there isn't, go to the database and get a count out.
* combine all these stats together
* get the names/template types etc out of the DB at the end.

app/dao/notifications_dao.py

@@ -50,7 +50,7 @@ from app.utils import convert_utc_to_bst, get_london_midnight_in_utc
 
 
 @statsd(namespace="dao")
-def dao_get_template_usage(service_id, limit_days=None, day=None):
+def dao_get_template_usage(service_id, *, limit_days=None, day=None):
     if bool(limit_days) == bool(day):
         raise ValueError('Must filter on either limit_days or a specific day')
 
@@ -75,8 +75,9 @@ def dao_get_template_usage(service_id, limit_days=None, day=None):
     ).group_by(
         Notification.template_id
     ).subquery()
+
     query = db.session.query(
-        Template.id.label('template_id'),
+        Template.id,
         Template.name,
         Template.template_type,
         Template.is_precompiled_letter,

app/dao/templates_dao.py

@@ -2,7 +2,6 @@ from datetime import datetime
 import uuid
 
 from sqlalchemy import asc, desc
-from sqlalchemy.sql.expression import bindparam
 
 from app import db
 from app.models import (
@@ -124,25 +123,16 @@ def dao_get_template_versions(service_id, template_id):
     ).all()
 
 
-def dao_get_templates_for_cache(cache):
-    if not cache or len(cache) == 0:
-        return []
-
-    # First create a subquery that is a union select of the cache values
-    # Then join templates to the subquery
-    cache_queries = [
-        db.session.query(bindparam("template_id" + str(i),
-                                   uuid.UUID(template_id.decode())).label('template_id'),
-                         bindparam("count" + str(i), int(count.decode())).label('count'))
-        for i, (template_id, count) in enumerate(cache)]
-    cache_subq = cache_queries[0].union(*cache_queries[1:]).subquery()
-    query = db.session.query(Template.id.label('template_id'),
-                             Template.template_type,
-                             Template.name,
-                             Template.is_precompiled_letter,
-                             cache_subq.c.count.label('count')
-                             ).join(cache_subq,
-                                    Template.id == cache_subq.c.template_id
-                                    ).order_by(Template.name)
+def dao_get_multiple_template_details(template_ids):
+    query = db.session.query(
+        Template.id,
+        Template.template_type,
+        Template.name,
+        Template.is_precompiled_letter
+    ).filter(
+        Template.id.in_(template_ids)
+    ).order_by(
+        Template.name
+    )
 
     return query.all()